Approximately 7 million Americans have what is known as non-valvular atrial fibrillation involving complications with the left atrial appendage of the heart (hereinafter, “LAA”). The LAA is a small, windsock shaped sac in the muscle wall of the left atrium.
Though uncertain as to what function the LAA performs, if anything, what is certain is that in patients with non-valvular atrial fibrillation, 90% of the thrombus formation occurs in the body of the LAA. In normal conditions, electrical impulses that control a heartbeat travel in an orderly fashion throughout the heart. These electrical impulses cause the heart to contract wherein blood in the left atrium and LAA is driven into the left ventricle with each heartbeat. However, in patients with atrial fibrillation the electrical impulses are fast and chaotic, wherein many impulses begin at the same time and spread throughout the atria. For instance, a healthy atria contracts 60-80 times per minute, while a fibrillating atria quivers at 300-400 times per minute. Problems arise when the electrical impulses do not allow the atria enough time to fully contract and efficiently displace blood into the left ventricle from the left atrium and LAA. Consequently, blood pools and collects in the LAA due to inefficient contraction of the atria and the LAA's sac-like physiological structure, causing blood clots. Strokes may ultimately occur in patients when the blood clots are pumped out of the heart and embolize to the brain. Notably, individuals with atrial fibrillation are five to seven times more likely to have a stroke than the general population.
Treatment of atrial fibrillation typically involves oral anticoagulant therapy. Patient's taking blood thinners have noted a reduction in the risk of stroke by 65% as compared to patients without medication. The oral anticoagulant warfarin (COUMADIN®) has been traditionally utilized to minimize thrombus formation in patients with atrial fibrillation. Due to the requirement of frequent blood draws to monitor a patient's anticoagulation status, frequent interactions of the medication with either dietary changes or with other medications, and the high risk of encountering serious bleeding events, Coumadin has recently fallen into disfavor in the medical community. Newer medications including dabigatran (PRADAXA®) and rivaroxaban (XARELTO®) are also being utilized. The advantage of these newer medications are that they have less interaction with dietary changes and do not require blood draws to monitor a patient's anticoagulation status. However, these medications continue to encounter serious gastrointestinal bleeding events, are not reversible, and are extremely expensive.
Patients who cannot tolerate anticoagulants, or are not eligible for anticoagulant treatment due to pregnancy or other medical reasons, may elect to undertake various procedures to seal off or remove the LAA. One particular procedure, known as LAA occlusion, involves implanting a device into the heart that closes the LAA. Currently, there are several different occluder devices on the market or in current testing, including the WATCHMAN®, ATRICLIP®, PLAATO LAA Occlusion System®, AMPLATZER™, and the AMULET™. In each of these devices, the major technical difficulty encountered is to get the device to reliably fix itself within the LAA without embolizing or migrating out of the LAA into the systemic circulation. The reason for this is multifactorial, although primarily being related to the LAA coming in many different sizes and configurations. Some sizes and configurations of the LAA are more amenable to device closure, whereas in others, device closure can be extremely difficult—if not impossible—to safely place an occluder device within the LAA.
The heart is comprised of three layers: (1) an inner endocardium layer; (2) a middle myocardium layer; and (3) an outer epicardium layer. The endocardium is a fragile, thin layer of tissue that lines the heart's chambers and valves. The myocardium is the thickest layer of the heart and is comprised of muscle tissue. The epicardium is a thin layer of visceral tissue. Between the heart and mediastinal space is the pericardium. The pericardium is a visceral layer of endothelium. The pericardial space lies in between the heart's epicardial surface and the pericardium. The pericardial space is filled with clear fluid that minimizes friction between the heart and other structures within the chest wall.
Current LAA occluder devices such as the WATCHMAN® and AMPLATZER™ have barbs on the outer edge of the device that latch on circumferentially to the endocardium layer of the LAA. Using barbs to fix the occluder device onto the endocardium layer of the LAA has significant disadvantages. For example, successfully “latching” an occluder device onto the endocardial layer of the LAA may be extremely difficult and time consuming for the interventional cardiologist. Problems are compounded if initial placement of the occluder device within the LAA is less than ideal, as the occluder device cannot be fully retrieved back within the delivery system without permanently damaging the retention barbs and/or the endocardium layer. Moreover, if the occluder device embolizes out of the LAA, irreparable damage to neighboring structures such as the mitral and/or aortic valves of the heart may occur in part, due to the presence of the barbs on the occluder device. Retrieval of an embolized occluder device is further complicated by the presence of the retention barbs.
Therefore, what is needed is an anchoring system and method for implanting an occluder device in the LAA that would allow for complete retraction and removal of the occluder device without permanently damaging the device. What is also needed is an anchoring system and method for implanting an occluder device in the LAA that provides a low risk of embolization and/or causing injury to neighboring valve structures. What is further needed is an anchoring system and method for implanting an occluder device that allows the occluder device to be positioned in multiple locations within the LAA, being able to be used in all types of LAA anatomy, and still result in optimal final placement of the occluder device within the LAA.